Where the manufacture of a workpiece calls for a plurality of work operations, then, for the economic production of the sheet-metal part, the necessary individual operations are conducted in a so-called transfer press or press line. The number of dies then corresponds to the number of work stages which are necessary for the manufacture of a multi-stage drawn part. Multiple-die or transfer presses of this type possess a transport device with which the workpieces are transported onward from one work station to the next. The longitudinal and transverse motions which are controlled by means of cam gears and any lifting motions of the transport device are derived from the primary drive and are thus synchronized with the ram motion. The basic structure of such a drive is represented in EP 0 210 745, FIG. 4. The traditional transfer system therefore practices the following functions in, respectively, two directions: gripping (transverse motion), lifting (vertical motion), conveyance (longitudinal motion).
In the manufacture of large-area sheet-metal parts, in particular, customary 3-axial transfer presses could no longer satisfactorily fulfill the holding and transport functions of the parts, since these large parts would sag too severely when transported in the gripper pliers. The so-called suction beam transfer systems were therefore developed as an alternative, in which large sheet-metal parts are fastened by means of a vacuum suction device to so-called suction beams. The suction beams or cross-ties are fastened to the supporting rails running through the transfer press, so that the transverse motion of the 3-axis system to grip the workpieces is no longer necessary. Since these suction beams, during the press cycle, cannot however travel outwards like the gripper rails in 3-axis operation with their transversely directed closing and opening motion, in this suction beam transfer a parking position for the suction beams has to be created, into which the suction beams are transported during the actual machining cycle.
In place of the longitudinal motion of the supporting rails for longitudinal transport, driven slides, trolleys or the like can also be disposed on the supporting rails, to which the cross-ties are fastened by suction devices (DE 38 24 058 C1). In this case, the supporting rails perform only a lifting motion during the transport cycle, whilst the longitudinal motion of the suction beams is effected by the slides.
Both in the 3-axis transfer of the workpieces using gripper rails and in the 2-axis transfer using supporting rails and suction beams, it is generally necessary to deposit the workpieces between the individual machining stations in so-called intermediate stations or orientation stations, which are generally located in the region of the uprights of the transfer press. In these orientation stations, the position of the workpiece can be changed in order to adapt it to the next machining stage (DE 38 43 975 C1).
The sheet-metal parts to be machined, which are becoming increasingly larger, led to the further development of the multiple-die or transfer presses into so-called large-part multiple-die presses (LP-presses), which are basically similarly constructed with the difference that, as a condition of the die size and workpiece size respectively, the transport steps turn out to be substantially larger. The use of multiple-die presses or large-part multiple-die presses accordingly enables a high production capacity, since all production steps necessary for the manufacture of a workpiece are simultaneously conducted. With each ram stroke a part is completed, irrespective of the number of work stations necessary for the manufacture in the individual case. A comparison with conventional press lines having individual presses reveals the advantage therefore, in multiple-die presses, of more compact introduction plant, lower energy costs and investment costs, as well as lower non-productive times in changing the die and in the conversion cycle.
Multiple-die presses of the stated type have the drawback, however, that a forced interlinking of all machining stations is necessary. The workpieces are guided at a specific machining rhythm through the multiple-die press, longer transport paths and hence longer transport times between the individual machining cycles being generated in respect of large-area parts and large dies associated therewith, since all press rams perform the machining cycle synchronously and simultaneously. An individual, out-of-phase and hence time-saving handling of the workpieces within the press is not therefore possible. In order to exert the high forces associated with simultaneous pressurization of the ram, the press has to be made correspondingly large.
In the known 2-axis or 3-axis drives, it is also disadvantageous that the insertion heights in the die stages are not variable, since the supporting or gripper rails can only execute a common stroke. Furthermore, as a result of the continuously common feed drive, an out-of-phase of-phase working of the die stages is not possible, which, especially where there is a large distance between the stages, owing to the long transport paths, produces poor freedom of passage.
The object of the invention is to avoid the above-stated drawbacks and, in particular, to obtain the most universal transfer drive possible for a multiple-die press and, in particular, a large-part multiple-die press or a press line or the like.